1. Field of the Invention
The present invention relates generally to spin valve sensors for magnetic heads, and more particularly to plasma smoothing of the pinned magnetic layer surface of a spin valve sensor structure.
2. Description of the Prior Art
Magnetic heads for hard disk drives typically have a read head portion including a magnetoresistive (MR) spin valve sensor structure for reading data from the disk of the hard disk drive. As is well known to those skilled in the art, such MR sensor structures include a plurality of thin film layers disposed between two magnetic shields that define the read gap. The thin film layers have particular magnetic properties, and are sensitive to the magnetic field of the data bits on the hard disk.
The thin film layers of a typical MR spin valve sensor will include at least one antiferromagnetic layer, at least one pinned magnetic layer, a spacer layer and at least one free magnetic layer. When the magnetic field direction of the free magnetic layer is parallel to the magnetic field direction of the pinned magnetic layer, the electrical resistance R of the MR sensor is lowest. When reading data, a magnetic data bit of a hard disk will cause the magnetic field direction of the free magnetic layer to change, whereupon the electrical resistance of the sensor increases. This change in resistance (ΔR) affects the electrical current passing through the sensor, which is thus detected as a data signal.
It is desirable to develop MR sensors having a decreased thickness, while maintaining or even increasing the ΔR value. Where the metallic MR sensor layers, and particularly the spacer layer, are made thinner, the electrical resistance of the thinner layers increases and there is less shunting of electrical current through these layers and away from the free magnetic layer. This leads to an increase in the sensor resistance R and in ΔR, and this results in improved magnetic head performance. Another parameter that is significant in spin valve sensor performance is the magnetic coupling field strength between the pinned and free magnetic layers, and it is important to maintain this coupling field strength to maintain the spin valve performance.
Many different materials and fabrication steps have been utilized in the prior art in attempts to increase ΔR of the MR sensor. The present invention relates to a MR spin valve sensor that is fabricated utilizing a surface smoothed pinned magnetic layer. This allows the use of a thinner spacer layer, thus leading to an increased electrical resistance R of the sensor and a higher ΔR, which correlates to a stronger read head signal.
It has been described in an abstract of prior art paper entitled “Effect of Plasma Treatment on the GMR Properties of PtMn Based Synthetic Spin Valve,” by K. Tsunekawa, D. Nakagima and N. Watanabe, presented as paper BD-04 at the 46th Annual Conference on Magnetism and Magnetic Materials, in Seattle, Wash., USA on Nov. 12-16, 2001, that with respect to a GMR spin valve sensor, that the surface of a pinned magnetic layer can be smoothed utilizing a low voltage argon plasma. A copper spacer layer and a free magnetic layer are then deposited. The resulting GMR sensor was shown to be improved by having an increased signal strength.
The present invention is an improvement upon this prior art in that it's utilizes an improved plasma comprised of argon plus oxygen, and that it utilizes an MR head having a CuOx spacer layer between the pinned and free magnetic layers.